1. Field of the Invention
The present invention relates to a water jet propulsion watercraft including a jet propulsion device driven by an engine, in particular, an internal combustion engine.
2. Description of the Related Art
A water jet propulsion watercraft according to one prior art is disclosed in Japanese Unexamined Patent Application Publication No. 11-208591 (1999). The water jet propulsion watercraft is a personal watercraft that obtains a propulsive force from a jet propulsion device driven by an internal combustion engine. The jet propulsion device is arranged to draw in water from around a hull, jet the water, and apply a reaction force obtained by the jetting to the hull.
The engine includes a combustion chamber in which fuel is combusted, an exhaust valve opening and closing an exhaust port, and an intake valve opening and closing an intake port. The exhaust gas exhausted from the combustion chamber passes through the exhaust port. Air that is made to flow into the combustion chamber passes through the intake port. An exhaust channel is connected to the exhaust port. The exhaust gas is discharged to an exterior of the hull through the exhaust channel.
In Japanese Unexamined Patent Application Publication No. 11-208591 (1999), it is described that an overlap period, in which the intake valve and the exhaust valve are opened simultaneously, is provided to increase exhaust pressure and increase engine output.